chemical changes 4

Question 1

what is the PH scale

Answer 1

a measure of how acidic or alkaline a solution is
the lower the PH the more acidic
the higher the more alkaline

Question 2

what is indicator

Answer 2

a dye that changes colour depending on weather it’s above or below a certain PH
some indicators contain a mixture of dys that means they gradually change colour over a broad range of PH

Question 3

ways to measure PH

Answer 3

PH probe

measure electronically

Question 4

what is an acid

Answer 4

a susbstance that forms aqueous solutions with PH of less than 7
Acids form H plus ions

Question 5

what is a base

Answer 5

a substance with a PH level greater than 7

Question 6

Base(alkali)

Answer 6

base that dissolves in water to form a solution with PH greater than 7
form OH minus ions

Question 7

acid + base =

Answer 7

salt + water

Question 8

H plus + OH minus =

Answer 8

H2O

Question 9

what do reactions of strong acids and alkali help calculate

Answer 9

reactions of a strong acids and alkalis to calculate the concentration by titration

Question 10

what PH does a neutral substance have

Answer 10

PH 7

Question 11

what do strong acids do in water

Answer 11

ionise completely in water

all acid particles dissociate to release H plus ions

Question 12

what do weak acids do in water

Answer 12

do not fully ionise

only a small proportion of particles dissociate to reales H plus ions

Question 13

what kind of reaction is a weak acid

Answer 13

reversible reaction which sets up an equillibrium between the undissociated and dissociated ions.
lies on the left because only few H plus ions are released

Question 14

what happens when the concentration of H plus ions increase

Answer 14

rate of reaction will be faster if strong acid

Question 15

what is the PH of acid or alkali and what happens when the scale decreases

Answer 15

a measure of the concentration of H plus ions

for every decrease of 1 on the PH scale the concentration increases by a factor of 10

Question 16

general rule when ion concentration changes

Answer 16

factor h plus ion concentration changes by 10-x (x is difference in PH)

Question 17

what does acid strength tell you

Answer 17

what proportion of the acid molecules ionise in water

Question 18

what is acid concentration

Answer 18

how much acid there is in a certain volume

Question 19

metal oxides or metal hydroxide + acid =

Answer 19

salt + water

Question 20

how you make a salt

Answer 20

metal + acid

Question 21

acid + metal carbonate =

Answer 21

salt + water + carbon dioxide

Question 22

what is the reactivity series

Answer 22

lists metals in order of their reactivity

Question 23

how is metal reactivity measured

Answer 23

how easily they lose there electrons and form positive ions

Question 24

acid + metal =

Answer 24

salt + hydrogen

Question 25

how do you measure reactivity

Answer 25

react it with an acid | the speed of the reaction is indicated by the amount of hydrogen gas given off

Question 26

metal + water =

Answer 26

metal hydroxide + hydrogen

Question 27

what is a redox reaction

Answer 27

a reaction that separates a metal from it's oxide

Question 28

Formation of metal ore =

Answer 28

Oxidation = gain of oxygen

Question 29

extraction of metal ore =

Answer 29

Reduction = loss of oxygen

Question 30

how is metal extracted with carbon

Answer 30

by reduction | ore is reduced as oxygen is removed from it and carbon gains oxygen so is oxidised

Question 31

how are metals higher than carbon extracted

Answer 31

electrolysis

Question 32

how are metals below carbon extracted

Answer 32

reduction using carbon

Question 33

what is oxidation

Answer 33

a loss of electrons

Question 34

what is reduction

Answer 34

a gain of electrons

Question 35

OIL RIG

Answer 35

oxidation is loss reduction is gain

Question 36

what are displacement reactions

Answer 36

involve one metal kicking another one out of it's compound

Question 37

rule of displacement reaction

Answer 37

A more reactive metal will displace a less reactive metal

Question 38

what gains the electrons and what loses the electrons during a displacement reaction

Answer 38

``` metal ion (reduced) metal atom (oxidised) ```

Question 39

what is an ionic equation

Answer 39

only show particles that react and the products produced not the spectator ions

Question 40

what and how does electrolysis do/work

Answer 40

an electric current is passed through an electrolyte positive ion in the electrolyte will move towards the cathode and gain electrons negative ions in the electrolyte will move towards the anode and loses electrons this creates a flow of charge through the electrolyte as the ions travel to the electrode

Question 41

why electrolysis only works on molten ionic solids

Answer 41

ionic solid can't be electrolysised because ions are in a fixed position and don't move molten ionic compounds can be electrolysed because the ions can move freely positive ions are reduced to the element at the cathode negative ions are oxidised to the element at the anode

Question 42

how is aluminium extracted using electrolysis

Answer 42

aluminium is extracted from the ore bauxite by electrolysis aluminium oxide has a very high melting temperature so it's mixed with cryolite to lower the melting point The molten mixture contains free ions the positive 3 plus AL ions are attracted to the negative electrode where they pick up three electrons and turn into neutral aluminium atoms the negative 2 minus O ions are attracted to the positive electrode where they each lose two electrons

Question 43

overall equation of extracted aluminium

Answer 43

aluminium oxide = aluminium + oxygen

Question 44

what do half equations show

Answer 44

show the reactions at the electrodes.

Question 45

electrolysis of aqueous solutions what else is produced

Answer 45

as well as the ions produced from the compound there will be hydrogen ions and hydroxide ions from the water. at the cathode if the hydrogen ion is less reactive than the metal hydrogen gas is formed otherwise the metal ion coats the cathode at the anode if hydroxide ions are present, molecules of chlorine, bromine or iodine will be formed if no halide ions are present then the hydroxide ions are discharged and oxygen will be formed

Question 46

reactivity series

Answer 46

``` potassium k sodium Na lithium Li calcium Ca magnesium Mg carbon C zinc Zn iron Fe hydrogen H copper Cu ```